We plan to study the thermodynamics of dissociation of the dimeric phospholipase A2 from rattlesnake (Crotalus atrox) venom with the aim of understanding better the relations between protein structure observed in crystallographic studies and solution thermodynamic properties. In the proposed experiments we plan to examine the pH, ionic strength, urea, and temperature dependencies of dissociation in order to determine the nature of the interacting ionizable resi dues and separate these thermodynamics from the contribution of H-bonds and solvation energies. The thermodynamic studies proposed also iclude the investigation of a complex formed between Pacific halibut muscle D-glyceraldehyde-3-phosphate dehydrogenase and phosphoglycerate kinase in the presence of substrates. We plan to elucidate which substrate or product is the effector of complex formation and determine the linkage relations between this compound(s) and complex formation. If feasible, the pH and temperature dependence of the equilibria will be examined as well. Our proposed work in the area of hydrodynamics is based on the thesis that continuum hydrodynamic properties apply at the atomic level to such small macromolecules as proteins. For the immediate work we plan to find the more correct treatment of rotational friction coefficients using the shell of beads model. The current theory neglects the rotations of the beads about their centers during the rotation of the shell model. When applied to the rotation of ellipsoids of revolution this theory should give the exact result at infinitessimal radius for the beads. The next stage in the project is to apply the theory to proteins for which crystallographic and rotational friction data are available. In order to use the theory for modeling proteins of unknown structure, it is necessary to develop a measure of protein surface rugosity. The method we propose to use involves "cutting" the protein into domains and using the properties of the inertia tensor determine the best ellipsoid enclosing the surface. This allows one to measure the mean surface deviation from a smooth object.